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1. Field of the Invention
In general the invention relates to fastening circuit boards to an electronic device. In particular the invention relates to a rack with board holders, which is used for fastening circuit boards by sliding them on place between board holders in a direction which is parallel with two edges of the circuit board. In addition, the invention relates to a device and a method for manufacturing board holders to a rack.
2. Description of the Related Art
Many modern electronic devices are mounted in a rack, whereby a typical prior art construction follows the principle shown in FIG. 1. A rack includes board holders fastened to horizontal shelves or vertical walls, between which the edges of the circuit board 100 are placed. In FIG. 1, the board holders are fastened to horizontal shelves, whereby there is a lower holder 101a for the lower edge of a board on the lower shelf, and an upper holder 101b for the upper edge on the upper shelf. There are connectors 102 on the board on the edge which goes in first when the board is pushed in place. The back wall of the rack is formed by the mother board 103, on which there are counterparts 104 for the connectors. When the card is pushed in place, the connectors 102 meet the counterparts 104, whereby the card is electrically connected to the mother board and through it to other boards of the same device. The number of boards in a certain device can be selected when the device is designed. Often the devices form families in which mother boards which are similar or nearly similar can be provided with a smaller number of boards for implementing a simple version, or with a larger number of boards for implementing a more versatile version.
Some prior art board holders will be briefly described in the following. FIG. 1 shows separate board holders 101a and 101b made of metal or plastic, which are fastened to a shelf (or wall) generally by means of bungs or screws. They have the drawback that they are separate parts, and their number, dimensioning and other properties must be compatible with both the boards and the shelves, which causes a logistic problem in the assembly of the devices. FIG. 2 shows board holders used in connection with shelves made of metal sheet, which are bent of the shelf metal. The board holder 201 comprises two tongues 201a and 201b reaching outward from the level of the shelf surface, which are formed by making a die cut shaped like a wide H, from which the rectangular areas that remain between the lines of the H are bent about 90 degrees around an imaginary axis which combines the ends of the vertical lines of the H. Many consecutive board holders like this can be formed to support the edge of one card. These board holders have the drawback of sharp edges, which can damage the card or injure the fingers of the person who assembles or services the device. The other type of board holder shown in FIG. 2 consists of two elongated, raised pieces of metal sheet 202a and 202b, which are formed by making four parallel, straight cuts on the shelf metal. The area between two adjacent cuts is forced to an upraised position. These upraised strips are arranged in consecutive pairs, whereby the edge of the card is always placed between two adjacent strips. In this type of board holder the edges can also remain dangerously sharp. In addition, the board holders shown in FIG. 2 have the drawback that both the upper and lower edge of the board do not always settle easily between the holders, but a part of the board may remain outside the holder, whereby the assembly of the device does not succeed.
An American registered design document number Des. 380,455 discloses a board holder according to FIG. 3, design protected by Metro Industries Inc., which is intended for use as the wall of a transport and storage shelf on which circuit boards are stored and/or transported during manufacture. The whole wall surface is covered by embossments 301 formed at regular distances, the shape and mutual placement of which is such that the board can be pushed on place either horizontally (arrow 302), diagonally downwards (arrow 303) or diagonally upwards (arrow 304). A solution of the same type is known from the U.S. Pat. No. 4.382,517. This solution is shown in FIG. 4. The surface of the wall panel comprises a number of diamond-shaped embossments 401, which form diagonal grooving on the whole wall surface for the edged of the boards. In the board holders shown in FIGS. 3 and 4, both the problem of separate parts and sharp edges have been solved, but the solutions are not suitable as board holders of racks, because they would require either a diagonally placed mother board or counterparts for the board connectors fastened diagonally on the mother board, and these are not known in the prior art. If it were assumed by way of example that the solutions were suitable for racks, there would also be the problem that when the grooves are near each other, it is possible to push the card into the wrong groove by accident, and that would damage the connection between the board and the mother board. There will also be the problem of insufficient bending stiffness of a shelf with board holders, if the solution shown in FIG. 3 or 4 were used on a shelf surface instead of a wall surface. Many boards with their components can be rather heavy, and if there are, for example, over 20 boards on a shelf which is 60 cm wide, their weight easily bends the lower shelf to an arched shape, whereby the upper edges of the boards in the middle may be detached from the upper holders. It would also be difficult to add ventilation holes to the board holders shown in the FIGS. 3 and 4 to ensure sufficient circulation of cooling air.
It is an objective of the present invention to provide a rack with board holders which can be manufactured by simple methods, which is safe in use and in which it is difficult to install the boards incorrectly. It is also an objective of the invention that the board holder would contribute to making the rack more rigid. In addition, it is an objective of the invention that a rack made according to it can easily be scaled to provide different distances between boards. Furthermore, it is an objective of the invention that the rack can have both board holders and ventilation holes.
The objectives of the invention are achieved by forming bubble-like embossments on the shelf or wall material, between which there are depressions for the edges of the board and which have two parallel edges in a direction which differs substantially from the direction intended as the direction of the edge of the board.
The rack according to the invention is characterized in that in order to support the first edge of the circuit boards, the first level surface of the rack comprises protruding embossments of the same material as the level surface, whereby the first embossment is between the point intended to support the first edge of the first circuit board and the point intended to support the first edge of the second circuit board, and that the extent of the embossment, perpendicular to the surface of the circuit boards, is the same as the distance between the circuit boards, and that the embossment has two parallel edges the direction of which differs substantially from the direction which is the intended direction of the first edge of the circuit boards.
The invention also relates to a device for manufacturing a board holder. The device according to the invention is characterized in that its working surface comprises a formation shaped like the letter H for forming two halves of an embossment delimited by the lines of the H on a level surface at one strike.
In addition, the invention relates to a method for manufacturing a board holder. The method according to the invention is characterized in that the working surface used in it comprises a formation shaped like an H, in which there are two parallel lines pointing in one direction, two parallel lines pointing in the opposite direction and a transverse line between the parallel lines pointing in opposite directions, whereby the method comprises striking the level surface with the working surface once, moving the working surface in relation to the level surface in the direction of the parallel lines of the H for a predetermined distance, and striking the level surface with the working surface again, whereby an embossment is formed on the level surface, delimited by the pattern left on it by the parallel lines of the H pointing in one direction at the first strike and by the pattern left on it by the parallel lines of the H pointing in the other direction at the second strike.
According to the invention, bubble-like embossments are formed on the shelf or wall of a rack at regular distances. The distances between the embossments are made such that the edge of a board having a certain thickness can be placed between two adjacent embossments. The width of the embossments corresponds to the distance between two adjacent boards used in the device, whereby no such point where the edge of the board might stay in the wrong position remains beside any board holder (between the embossments). The height of the embossments from the surface of the shelf is selected such that a bend of an assumed magnitude in the lower shelf is not sufficient to release the upper edge of the boards in the middle of the shelf from the embossments which act as the board holders above.
The preferred material for the shelf is stainless steel, which provides many advantages. A shelf made of stainless steel has excellent corrosion resistance. In addition, forming bubble-like embossments by forcing causes work hardening in stainless steel, and thereby improves the rigidity of the shelf. According to the invention, the bubble-like embossments extend over a substantial part of the width of the shelf, whereby the profile of the edges of the bubble-like embossments makes the shelf more rigid especially because of the work hardening but also because of its shape.
The bubble-like embossments according to the invention are formed on the shelf preferably with a tool which has an H-shaped working surface. This provides the advantage that the same tool can be used to form bubble-like embossments of different widths, or board holders suitable for different distances between boards by moving the tool for making the adjacent embossments for a distance in which the parallel lines of an H-shaped working surface partially overlap in two successive shaping steps. The manufacturing costs of a tool like this are considerable, and therefore is particularly advantageous that different tools need not be manufactured for different distances between boards.
The middle part of a bubble-like embossment according to the invention can be removed, whereby the hole provides ventilation. This does not have a considerable negative effect on the above mentioned advantageous features of the inventions, such as the rigidity of the shelf.